The present invention relates to an anode including a particulate anode active material and a binder and a battery using it, and manufacturing methods thereof.
A secondary battery is utilized as a portable power source for various portable electronic devices or portable communication equipment such as a combination camera and a laptop computer. In recent years, downsizing, weight saving, and high performance of these portable electronic devices and portable communication equipment have been made significantly. Along with these situations, improvement of characteristics of the secondary battery has been strongly aspired. Specially, a lithium ion secondary battery has attracted attention, since the lithium ion secondary battery can provide a larger energy density compared to a lead battery or a nickel-cadmium battery, which is a conventional aqueous solution-type electrolytic solution secondary battery.
Conventionally, in this lithium ion secondary battery, as an anode material, carbonaceous materials such as non-graphitizable carbon and graphite showing a comparatively high capacity and realizing good charge and discharge cycle characteristics have been widely used. However, along with recent trend of high capacity, acquiring even higher capacity of the anode has been aspired, and the research and development thereof has been promoted.
To cite a case, for example, a technique, in which a high capacity is attained by an anode using a carbonaceous material by selecting a carbonized raw material and fabrication conditions has been reported (for example, refer to Japanese Unexamined Patent Application Publication No. H08-315825). However, when this anode is used, a discharge potential is 0.8 V to 1.0 V in relation to lithium. Therefore, a battery discharge voltage when the battery is constructed becomes low, and therefore, major improvement with respect to a battery energy density cannot be expected. Further, there are shortcomings that hysteresis is large in a charge and discharge curve shape, and energy efficiency in each charge and discharge cycle is low.
Further, as an anode material capable of realizing a higher capacity, for example, a material applying a fact that a certain kind of a lithium metal is reversibly generated and decomposed by an electrochemical reaction has been widely researched. Specifically, Li—Al alloy has been widely known from long time ago, and silicon alloy is also reported (for example, refer to U.S. Pat. No. 4,950,566). However, there are problems that the anode materials of these alloys and the like are highly expanded and shrunk due to charge and discharge, cracks or separation is generated in the electrode, pulverization phenomenon is generated, and charge and discharge cycle characteristics thereof are poor.
Therefore, in order to improve charge and discharge cycle characteristics, anode materials to which an element not involved in the expansion and shrinkage due to insertion and extraction of lithium is added have been reported. As such an anode material, for example, LivSiOw (v≧0, 2>w>0) (refer to Japanese Unexamined Patent Application Publication No. H06-325765), LixSi1-yMyOz (M is a metal except for alkali metals or a metalloid except for silicon, x≧0, 1>y>0, 0<z<2) (refer to Japanese Unexamined Patent Application Publication No. H07-230800), Li—Ag—Te alloy (refer to Japanese Unexamined Patent Application Publication No. H07-288130), and a compound including an element of Group 4B except for carbon and one or more nonmetallic elements (refer to Japanese Unexamined Patent Application Publication No. H11-102705) can be cited.
However, even when these anode materials are used, there are problems that as charge and discharge cycles are repeated, cracks or separation is generated in the electrode due to expansion and shrinkage of the material, electron conduction of the electrode lacks, and charge and discharge cycle characteristics are largely deteriorated. Therefore, even when a new high-capacity anode material is used, the characteristics thereof cannot be sufficiently demonstrated.